The invention relates to recording heads for use with magnetic storage media, and more particularly, relates to such recording heads with oppositely directed conductors for inducing a magnetic write field for longitudinal or perpendicular magnetic recording.
Longitudinal and perpendicular recording heads for use with a magnetic storage medium are generally known. Longitudinal recording heads utilize a pair of opposing write poles with their tips in close proximity to each other at the bottom surface of the recording head. The two poles are connected at the top by a yoke, which may be made of a ferromagnetic material similar to that used for the poles. A coil having a plurality of turns is located in close proximity to one of the two opposing poles. When a current is passed through the coil, magnetic flux is induced in the yoke, which produces a magnetic field across a write gap, which separates the two poles. A portion of the magnetic flux across the write gap passes through the magnetic storage medium, thereby causing a change in the magnetic state within the magnetic storage medium where the head field is higher than the medium coercive force. The medium coercive force is chosen high enough so that only the head fields across a narrow gap of a thin film inductive head, flowing with a slider on an air-bearing between the surfaces of the disc and the slider, modify the bits of information on the storage medium.
The bits of information are recorded on the disc along concentric tracks that are separated by guard bands. The width of the track plus that of the guard band in which no information is stored defines the track density. The length of the bit along the track defines the linear density. The total storage capacity is directly proportional to the product of track density and linear density. The recording densities possible with longitudinal recording are believed to be limited to approximately 50 to 100 Gbit/inch2, because at higher recording densities, superparamagnetic effects result in magnetic instabilities within the magnetic storage medium.
Perpendicular recording has been proposed to overcome the recording density limitations of longitudinal recording. Perpendicular recording heads for use with magnetic storage media may include a pair of magnetically coupled poles, including a main write pole having a small bottom surface area and a flux return pole having a large bottom surface area. A coil having a plurality of turns is located adjacent to the main write pole for inducing a magnetic field between that pole and a soft underlayer. The soft underlayer is located below the hard recording layer of the magnetic storage medium and enhances the amplitude of the field produced by the main pole. This in turn allows the use of storage medium with higher coercive force; consequently, more stable bits can be stored in the medium. In the recording process, an electrical current in the coil energizes the main pole, which produces a magnetic field. The image of this field is produced in the soft underlayer to enhance the field strength produced in the magnetic medium. The flux density that diverges from the tip into the soft underlayer returns to the main pole through the return flux pole. The return pole is located sufficiently far apart from the main pole such that the soft material of the return pole does not affect the magnetic flux of the main pole, which is directed vertically into the hard layer and soft underlayer.
Regardless of whether longitudinal or perpendicular recording is employed, the goal of higher recording densities requires higher data rate capabilities. However, recording heads, and specifically, the inductive write head portions thereof, are comprised of magnetic inductors. Such inductors behave as an electrical short for low frequency or DC signals, while they behave as an electrical open for high frequency signals. As a result, inductors become more and more difficult to pass current through as the drive frequency increases. Inductors are classified according to their inductance L, which scales the time change of current into induced electromotive force (EMF). This induced EMF is set up to oppose the flow of magnetic flux through the coil and its magnetic core, and hence reduces the efficiency of flux flow, according to the following formula:             V      EMF        =          L      ·                        ⅆ          I                          ⅆ          t                      ,
where VEMF is the opposing voltage, L is the inductance, I is the driving current, and dt is the change in time. A write head must balance the need for magnetizing field, which traditionally requires large magnetic flux, against the need for efficiency, which is reduced because inductors resist being magnetized according to the above formula (they slow down the circuit response). Increasing the flux to get a larger field has the detrimental side-effect of also increasing L. For a given L, the faster one tries to turn on the current, the larger the induced EMF which acts to cancel the induced field, and hence the less efficient the head is. Therefore, to have a head function at high data rates, where dt is very small, L must also be made correspondingly small to balance dt. However, the head must still produce enough field to write. It is well-known that the majority of the head field comes from the soft magnetic core rather than the field of the electrical coils. However, the self-inductance of a conventional coil scales with the square of the number of turns: i.e. a 6 turn head has 36 times more inductance than a 1 turn head, assuming the core inductance is constant. If the single turn head can drive enough flux through the magnetic core to magnetize it and produce sufficient write field, then a single turn head can decrease dt by 36 times compared with the 6 turn head. This analysis assumes that both heads are in a frequency regime where the L of the 6 turn head is large enough to limit the frequency response of the head. Obviously, if the desired dt is obtainable with small enough EMF that the head is sufficiently efficient, then there is nothing to be gained by reducing the inductance of the head.
There is identified, therefore, a need for an improved recording head for higher recording densities and increased data rates that overcomes limitations, disadvantages, or shortcomings of known recording heads.
The invention meets the identified need, as well as other needs, as will be more fully understood following a review of this specification and drawings.
In accordance with an aspect of the invention, a recording head for use with a magnetic storage medium comprises a pair of write poles and a pair of oppositely directed conductors located adjacent the pair of write poles. The pair of write poles are structured and arranged to apply a magnetic write field to the magnetic storage medium. The pair of oppositely directed conductors combine to induce the magnetic write field in the pair of write poles. One of the oppositely directed conductors has a positive voltage relative to ground and the other of the oppositely directed conductors has a negative voltage relative to ground. The oppositely directed conductors may be microstrip waveguides. In addition, the pair of write poles may be structured and arranged for either longitudinal or perpendicular recording. Advantageously, the pair of oppositely directed conductors combines to drive the magnetic write field in the same direction.
In accordance with an additional aspect of the invention, a magnetic disc drive storage system comprises a housing, a rotatable magnetic storage medium positioned in the housing, and a recording head mounted in the housing adjacent to the rotatable magnetic storage medium. The recording head comprises a pair of write poles with a connecting yoke therebetween, wherein the pair of write poles are structured and arranged to apply a magnetic write field to the magnetic storage medium. The recording head also includes a pair of oppositely directed conductors located adjacent the pair of write poles so as to combine to induce the magnetic write field in the pair of write poles. One of the oppositely directed conductors has a positive voltage relative to ground and the other of the oppositely directed conductors has a negative voltage relative to ground. Each of the oppositely directed conductors may be a microstrip waveguide. In addition, the pair of write poles may be structured and arranged for performing either longitudinal or perpendicular recording.
In accordance with a further aspect of the invention, a method of using a recording head to apply a magnetic write field to a magnetic storage medium is provided. The method includes positioning a pair of write poles, that are structured and arranged to apply the magnetic write field to the storage medium, adjacent the magnetic storage medium. The method further includes inducing the magnetic write field in the pair of write poles with a pair of oppositely directed conductors located adjacent the pair of write poles. The oppositely directed conductors combine to induce the magnetic write field in the pair of write poles due to one of the oppositely directed conductors having a positive voltage relative to ground and the other of the oppositely directed conductors having a negative voltage relative to ground. The method may further include employing as each of the oppositely directed conductors a microstrip waveguide.